Joel Makower is a widely respected writer and consultant on issues of sustainable business, clean technology and green markets. His essays on environmental business and technology are a regular feature of our Sustainability Sundays. Take it away, Joel:

How many Earths does it take to feed a continent?

A new report shows that Europe uses 20% of the biosphere's services to serve 7% of the world's population -- a resource demand that has risen nearly 70% since 1961.

Bad as that may sound, it's nothing compared to Americans' footprint on the planet.

The ecological footprint measures people’s demand on nature. A country’s footprint is the total area required to produce the food and fiber that it consumers, absorb its waste, and provide space for its infrastructure. Because people consume resources and “nature’s services” -- crop pollination, photosynthesis, the hydrologic cycle, and all the rest -- from all over their world, their footprint is the sum of these areas, wherever they are on the planet. (WorldChanging has coveredecologicalfootprints in detail in the past, and Alex has explored the "great wager" footprint overshoot implies. -- ed.)

Ecological footprints often are expressed in terms of the "number of Earths" it would take to provide the capacity needed to support a given population. The figure to the left, from the Global Footprint Network, shows the ratio between the world's demand and its capacity in each year, and how this ratio has changed over time. The horizontal blue line represents the one Earth that actually exists; the red line shows humanity's rising appetite in terms of the "number of Earths" needed to support humanity at current demands. This graph shows how we have moved from using, in net terms, about half the planet's biocapacity in 1961 to 1.2 times the biocapacity of the Earth in 2001. This represents a global "ecological deficit" of 0.2 "Earths."

This latest footprint report marks the first time Europe has ever tracked and studied its ecological spending in relation to planetary limits The result: Europe's consumption levels can continue to grow only by importing more natural resources -- such as wood, metals, or fish -- from other countries and dumping more of its greenhouse gas waste into the global atmosphere.

Among the key findings:

Europeans now require 4.9 globally average hectares per person to provide for their lifestyle. As the continent can only supply 2.2 global hectares per person, Europeans rely on the rest of the world to make up this increasing deficit. Europe's Ecological Footprint represents an area more than twice the size of Europe. (By contrast, Americans’ needs are nearly twice Europeans: 9.5 average hectares per person.)

Globally, humanity requires 2.2 global hectares of productive area per person to sustain current lifestyles, 1.3 times more than in 1961. But the Earth currently has just 1.8 global hectares available per person. This "overshoot" of 21% depletes the Earth's natural capital, and is thus possible only for a limited period.

From a low of 3.5 global hectares per Hungarian to a high of just over 7 global hectares per Swede, all of the EU members have footprints above the world's sustainable average, and all but three -- Sweden, Latvia, and Finland -- are in local ecological deficit.

The challenge isn't just environmental, but also economic. "While it is still cheap to run an ecological deficit, if humanity's current levels of resource consumption continue, such a deficit will become an increasing liability for countries," says Mathis Wackernagel, executive director of the Global Footprint Network and lead author of the report, "This deficit spending will jeopardize Europe's long-term prosperity if it is not seriously addressed."

The longer this deficit is left unchecked, says Wackernagel, the more expensive the investment required and the greater the risk that critical ecosystems will be eroded beyond the point at which they can easily recover. As Europe's and the world's ecological debt accumulates, choices narrow and present resource use becomes ever more dependent on liquidating ecological assets.

As any economist knows, you can only liquidate your assets to a point. Then you become bankrupt.